The inventors herein have recognized a need for an improved diagnostic system for a DC-DC voltage converter. The diagnostic system provides a technical effect of obtaining diagnostic diversity by sampling a first voltage at a first node of a high voltage bi-directional MOSFET switch in the DC-DC voltage converter using a common channel in a first bank of channels of an analog-to-digital converter, and then sampling the first voltage using the common channel in a second bank of channels of the analog-to-digital converter to determine fault conditions associated with the high voltage bi-directional MOSFET switch.